Bath for isothermal and step quenching of articles in salt and alkali melts



Sept. 3, 1968 v. N. BIRJUKOVA 3,399,877

BATH FOR ISOTHERMAL AND STEP QUENCHING OF ARTICLES IN SALT AND ALKALI MELTS Filed May 21, 1964 5 Sheets-Sheet 1 FIG. 3

Sept. 3, 1968 v. N. BIRJUKOVA BATH FOR ISOTHERMAL AND STEP QUENCHING OF ARTICLES IN SALT AND ALKALI MELTS 3 Sheets-Sheet 2 Filed May 21, 1964 lllllllllllfl"l I" I'll If,

Sept. 3, 1968 v. N. BIRJUKOVA BATH FOR ISOTHERMAL AND STEP QUENCHING OF ARTICLES IN SALT AND ALKALI MELTS Filed May 21, 1964 3 Sheets-sheet 5 FEEEFFLFELFFEFEEICkEEhLttFLtLFELFLr FIG. 4

United States Patent BATH FOR ISOTHERMAL AND STEP QUENCHING 0F ARTICLES IN SALT AND ALKALI MELTS Valentina Nickolaevna Birjukova, Gorky, U.S.S .R., as-

siggtg'Rto Gorkovsky Metallurgichesky Zavod, Gorky,

Filed May 21, 1964, Ser. No. 369,192 4 Claims. (Cl. 266-6) This invention relates to heat treatment of steels and alloys, and particularly to a tank for isothermal and step quenching thereof in salt and alkali melts.

Isothermal and step quenching is known to improve considerably the mechanical properties of steel, especially its toughness and durability. The life of an article thus treated is increased several times.

Quenching strains are thus reduced, and no quench cracks appear. However, despite its indisputable advantages isothermal and step quenching finds only limited use, mainly because of the inadequate cooling capability of salt or alkali melts, and also because there has been no known tank design which can enable effective cooling of the melt andsalt and alkali in which quenching is performed.

Tank arrangements are known in which the melts were cooled by high or low pressure air by tubes immersed into the melts, or by air blasting of the crucible walls and melt surface, or by cooling the crucible walls with water.

It was further known to introduce water into the salt or alkali melts to improve their cooling power, namely, water was added to the melt while it was made ready for use, in the amount of 2 to 6 percent of the salt weight, or 10 to percent of the alkali weight in the case of alkali melts. The melt would be thoroughly mixed with water, allowed to cool to harden and then melted again.

A disadvantage of known arrangement is their failure to withdraw the full amount of heat introduced into the melt by the quenched articles, or to ensure stable cooling power of the melt. Attempts to overcome these disadvantages brought no satisfactory solution. These problems, namely, the cooling of the melts and stability of the cooling power, are successfully solved by the present invention which has produced practical results.

It is an object of this invention to provide a tank which will permit cooling of the melt to a required temperature and to maintain its cooling power constant. Another object of the invention is to ensure full safety.

The invention is based on the requirement to develop a tank which will permit cooling the melt with water at any melt temperature and maintaining the water content of the melt within specified limits. Accordingly the invention is directed to a tank containing a melt for isothermal and step quenching of articles, provided with a cover having an inlet pipe for the supply of water onto the melt surface, as herein described and claimed in the present specification with the understanding that modifications may be effected by those skilled in the art Without departing from the principles and scope of the invention, and we do not limit ourselves to the particular details hereinafter set forth except as defined by the following claims. The objects and advantages of the invention will be understood from the following detailed description of a bath for isothermal and step quenching of articles in salt or alkali melts, with the accompanying drawings in which:

3,399,877 Patented Sept. 3, 1968 FIG. 1 is a diagrammatic side view of a tank with a cover to ensure a safe water supply into the melt;

FIG. 2 is a sectional view taken along line IIII of FIG. 1;

FIG. 3 is a detail on enlarged scale of a cover employed for water supply to the melt;

FIG. 4 is a sectional view taken along line IV-IV of the cover in FIG. 3.

The bath is contained in a tank 1 designed to hold salt or alkali melt.

The tank 1 is provided with a cover 2 having an inlet pipe 3 fixed therein. A disperser 4 is positioned underneath the said inlet pipe. The said cover is fixed onto a frame in the form of a casing with flanged rims 5 constituting a shield which overlaps the cover with a certain clearance between the said cover 2 and rims 5. The cover is placed above the melt surface, and its lower edge is immersed to a depth of about 50 mm. into the molten salt or alkali; the cover rests on two brackets 6 immersed in the melt and secured to the tank.

Inlet pipe 3 installed in the center of cover 2 feeds water to the disperser 4; the disperser sprays water over the surface. Some water becomes absorbed by the melt while the remaining water is immediately evaporated. The produced steam escapes through the gaps between the cover and the rims 5 of the frame, while the salt or alkali will remain on the inside surface of the cover and rims; thus bath escape is prevented and the operation is completely safe when water is supplied into the bath.

In case of a tank of large dimensions, several covers of the afore-described type may be provided above the melt surface, or a cover of larger size may be employed with the inlet pipe of a larger diameter.

The following illustration of the invention is given with the purpose that the invention may be better understood by those skilled in the art.

Illustration This invention was tested in quenching blades of shears of 950 x 165 x mm. manufactured of 6 x C steel (a chrome-silicon variety) the quenching being performed in a 8 cubic metre tank. The melt consisted of 55% KNO +45% NaNO +5 to 7% H 0, and had a temperature of 260 to 270 C. During 15-minute quenching of a quantity of blades weighing 1.5 tons altogether water was supplied at the rate of 6 litres per minute; the melt temperature did not vary, and the blades gained a hardness to 50 to 55 R What we claim is:

1. Apparatus for isothermal and step quenching of articles, comprising a tank for holding a salt or alkali melt; a cover having open ends and being positioned on the tank above at least a part of the surface of said melt and having its lower edge immersed in said melt; at least one water inlet pipe secured in said cover in such a manner as to direct water onto the surface of the melt; a frame including a shield, said frame being joined to said cover so as to provide steam escape gaps between the open ends of the cover and the shield.

2. Apparatus as claimed in claim 1 further comprising water dispersing means beneath said inlet pipe and above the surface of the melt for depositing dispersed water onto said melt.

3. Apparatus as claimed in claim 2 wherein said tank has a transverse extent and the cover extends the entire transverse extent of the tank.

3 4 4. Apparatus as claimed in claim 3 wherein said shield 2,150,437 3/1939 Gilbert. encircles said cover and includes a rim extending above 2,516,516 7/1950 Holden 2666X the cover in spaced relation. 2,618,284 11/1952 Purnell 266--4X FOREIGN PATENTS 606,734 8/1948 Great Britain.

References Cited UNITED STATES PATENTS 528851 11/1894 Caben 204 275X SPENCER OVERHOLSER, Primary Exammer.

2 12 534 193 Cope 2 R. S- ANNEAR, ASSiS/dllf Examiner. 

1. APPARATUS FOR ISOTHERMAL AN STEP QUENCHING OF ARTICLES, COMPRISING A TANK FOR HOLDING A SALT OR ALKALI MELT; A COVER HAVING OPEN ENDS AND BEING POSITIONED ON THE TANK ABOVE AT LEAST A PART OF THE SURFACE OF SAID MELT AND HAVING ITS LOWER EDGE IMMERSED IN SAID MELT; AT LEAST ONE WATER INLET PIPE SECURED IN SAID COVER IN SUCH A MANNER AS TO DIRECT WATER ONTO THE SURFACE OF THE MELT; A FRAME INCLUDING A SHIELD, SAID FRAME BEING JOINED TO SAID COVER SO AS TO PROVIDE STEAM ESCAPE GAPS BETWEEN THE OPEN ENDS OF THE COVER AND THE SHIELD. 